Project Summary Alzheimer?s Disease (AD) and Frontotemporal Lobe Degeneration spectrum diseases caused by tau (FTD-tau) are two neurodegenerative diseases that are characterized by accumulation of abnormal tau. It has been known for many years that tau does not accumulate in all cells in the brain despite the widespread expression of the tau gene. Some regions of the brain (and specific cell populations within them) are differentially vulnerable to accumulating pathological forms of tau. The reasons for this are unknown, and addressing this question is critical for AD and FTD, and also other neurodegenerative diseases showing selective vulnerability. We have observed that excitatory neurons (compared to inhibitory neurons) are especially vulnerable to tauopathy and, using a systems biology approach, have identified deficient tau homeostasis (proteostasis) as a likely mechanism. We now wish to extend these studies to a study on the impact of aging on tau homeostasis pathways in excitatory compared to inhibitory neurons, in human and mouse brain, and in a novel human-derived neuron model, testing one pathway (BAG3) that was implicated from the transcriptomics. Additionally, we will examine the selective vulnerability of neurons in patients with primary tauopathies associated with FTD. Lastly we will work with RNA datasets generated by Allen Institute to identify key pathway differences between excitatory and inhibitory neurons from the entorhinal cortex to begin to identify why excitatory and inhibitory cells might differ in their proteostasis capacity. These studies will explore the basis of selective vulnerability to tauopathy, generate well-characterized resources and potentially identify new disease causing pathways.